Do you know any hidden or little-known nice feature of Mac OS X? It doesn't matter what it is—maybe just a short terminal command or a keyboard shortcut. Share your experiences on hidden Mac OS X features with us..

Please post one tip per answer. Please also check to see if your answer has already been posted - duplicate answers will be deleted. To search answers for this question use inquestion:400 (or inquestion:this, directly from the question page) in addition to your search terms in the search box in the upper right hand corner of this page.

Also provide details on how to achieve that feature, and if possible, include a relevant image too!

Does iOS count? I'm sure most people know, but if you pull the camera thingy on the lock screen in iOS 7 up about 2/3 of the screen and then quickly flick it back down again, it will bounce up high enough to trigger the camera!
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RPi AwesomenessDec 27 '13 at 3:56

Switcher + Exposé

(10.6+)

While ⌘+⇥ing (holding ⌘, tapping ⇥), you can press ↑ or ↓ to switch to the currently selected application's window Exposé view. You can then use the keyboard arrows to highlight a window and ↩ to switch to it.

I had it posted on the Lion tips & tricks thread (now deleted from the thread) - apple.stackexchange.com/questions/18677/… - (I couldn't remember if it was possible on Snow Leopard) - BUT there this comment was written "This was in snow leopard as well" - so I don't now what right and wrong, because I don't have Snow Leopard anymore for testing - what I know is that it is working as described in Lion.
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Rene LarsenAug 2 '11 at 22:29

As of Mac OS X Lion 10.7, Terminal provides Services to do this. Enable New Terminal at Folder in System Preferences > Keyboard > Keyboard Shortcuts > Services. The quickest way to get there is to choose [Application Menu] > Services > Services Preferences…. There's also New Terminal Tab at Folder. These operate on folders in Finder, as well as pathnames selected in text in any application. You can also drag folders (and pathnames) onto the Terminal application icon in the Dock, or onto the tab bar of a terminal window to add a new tab.
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Chris PageSep 4 '11 at 9:30

When switching focus between applications, you can hold down ⌥ and click on another application. When you change focus from one application to another, the first application hides. So, let's say you are switching from an open Finder window to an open TextEdit window while holding the ⌥ key. Finder will hide once you click on the TextEdit window. I discovered this by accident and it's pretty cool

From man purge: “force disk cache to be purged (flushed and emptied). Purge can be used to approximate initial boot conditions with a cold disk buffer cache for performance analysis. It does not affect anonymous memory that has been allocated through malloc, vm_allocate, etc.”
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Mathias BynensMar 26 '12 at 7:44

3

To put it more bluntly, purge-ing your disk caches can actually slow you down.
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ziggJul 4 '13 at 22:43

I searched through all 5 pages of this thread and I'm surprised to find that nobody already mentioned this handy tip for Terminal.app:

Press ctrl+R to bring up a search through your command history. It's a somewhat fuzzy search in that what you're typing doesn't have to be the initial characters of a command, but it still must be a contiguous section of the command.

For example, you could find a previous usage of curl by typing "rl" in the search... or "post" if the curl command you want to find was a POST.

You can also use the Up & Down arrows to flip through just the matching commands in your history.

You can access the file, edit and other application menus with the "move focus to the menu bar" setting in Keyboard Preferences. I changed it from the default to ctrl ` as the default merely adjusted brightness.

To quickly lock your computer with a screen-saver style password, regardless of whether a password or time delay is set in the Security preference pane, enable the keychain status menu item and use its Lock Screen command. To enable it, open the Keychain Access utility, choose Preferences… from the Keychain Access menu, and enable "Show Status in Menu Bar" from the General pane.

@bot47 Not exactly the same. Ctrl-Shift-Eject simply puts the display to sleep. Therefore (1) the password lock does not kick in until the Security time delay is reached (if password is even enabled in the first place) and (2) the display goes to sleep instead of screen saver mode, which as of Lion requires a keyboard button press or mouse click to awaken and takes slightly longer to respond to user input.
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PCheeseNov 9 '11 at 0:52

3rd party apps can add unwanted items to your right click menus! To add or remove items from the right click contextual menus:
Go to System Preferences -> Keyboard -> Keyboard Shortcuts. Select the "Services" panel and uncheck the services which you don't need.

Ever wanted to stop the iTunes visualizer at that really cool moment and take a picture? In iTunes 10 (and previous versions really) you can control what your visualizer is doing. You need to have a song playing to notice changes.

Simply press the ? key to see a help menu of the controls. On most visualizers press f to see the current FPS. (all except the default)

To freeze the default iTunes visualizer press F to freeze the mode, then press L to freeze the camera. Now that your visualizer is completely stopped, press M to change the mode. Turn the fog on and off with N (only works with certain themes). Change the color palette with P before freezing the mode or locking the camera or it has no effect. ⌘ + F for full screen, then ⌘+⇧+3 for full screen grab.